Synthesis and structural characterization of 1-mesityl-1,3-dihydro- imidazole-2-selone and bis(1-mesitylimidazol-2-yl)diselenide: Experimental evidence that the selone is more stable than the selenol tautomer

1-Mesityl-1,3-dihydro-imidazole-2-selone, (seim^Mes)H, may be obtained from 1-mesitylimidazole via (i) deprotonation with BuⁿLi, (ii) treatment with elemental selenium, and (iii) addition of HCl(aq). Structural characterization of (seim^Mes)H by X-ray diffraction demonstrates that the compound exists as the selone rather than selenol tautomer, a result that is in accord with DFT calculations. Solutions of (seim^Mes)H are oxidized by air to give bis(1-mesitylimidazol-2-yl) diselenide, (seim^Mes)₂. A corresponding investigation of (seim^Me)H demonstrates that, in contrast to a previous report, the selenium analogue of methimazole exists in the selone form with a structure analogous to that of methimazole. ¹H and ⁷⁷Se NMR studies demonstrate that the (seim^R) groups of the selone (seim^R)H and diselenide (seim^R)₂ undergo facile exchange on the NMR time scale.